One problem which has been encountered in measuring the temperature of continuously moving surfaces is that conventional thermocouple measuring devices either cannot accurately measure the temperature of the moving surfaces or the thermocouple can only measure one particular point on the surfaces. This problem is enhanced in the extrusion of various materials, particularly the extrusion of metals. In the extrusion of materials, it is very desirable to maintain an extrusion temperature within a definite range which is below the lowest melting point of any component of the extruded material. This is particularly true in the extrusion of metal alloys, where there may be many components of each alloy, each component with its own melting point, so that the preferred extrusion temperature requires careful calculation and careful control of the extrusion apparatus.
One manner of measuring extrusion temperatures has been to insert a static thermocouple in the extrusion die itself. In some instances, the thermocouple is inserted in a hole which is drilled through the die so that the sensitive thermocouple end is in the same position as in one surface of the die. Therefore, the thermocouple is in actual contact with the extrusion material and measures the temperature of the material as it flows through the die. One of the problems with this arrangement is the difficulty in placing the thermocouple lead wires through the die holder and other tooling arrangements to an indicating device. The susceptibility of mechanical damage to these lead wires is extremely high and if the wires are pinched and shorted, the whole die assembly has to be taken apart for replacement of the measuring device. This arrangement utilizes a thermocouple of conventional design, i.e., two dissimilar metals welded together to form the heat-sensitive junction which then contacts the surface to be measured.
Another manner of measuring material which has been extruded through a die is that found in, for example, U.S. Pat. No. 3,155,237. This patent teaches an arrangement of thermocouple members placed a distance away from the die surface. The material being extruded must be electrically conductive since it forms part of the thermocouple junction, which generates the electromotive force necessary to move an indicator on a temperature dial. The thermocouple members are a pair of gripping tongs which grip the extruded material at an end distant from the face of the extrusion die. These gripping tongs contact the surface of the extruded material at this distant point to avoid damaging the surface of the extruded material adjacent to the die face. A problem which this approach engenders is the cooling of the extruded material between the die face and the distant point where the thermocouple tongs grip the extrusion. This approach will also indicate only the average temperature of the two points where the tongs are in contact with the surface. For example, if the temperature is 500.degree. F. at one contact point and 600.degree. F. at the other contact point, a temperature of 550.degree. F. will be indicated.
It is, therefore, a principal object of the present invention to provide an apparatus which can accurately measure the temperature of continuously moving surfaces and which can accurately measure the temperature along the length of a stationary surface.
It is a further object of the present invention to provide a means for accurately measuring the temperature of continuously moving surfaces or along the length of stationary surfaces without scratching or otherwise harming said surfaces.
It is still a further object of the present invention to provide a thermocouple means for accurately measuring the temperature of continuously moving surfaces or along the length of stationary surfaces which can be easily constructed and readily produced without great expense.
It is a still further object of the present invention to provide a thermocouple means for accurately measuring the temperature of extruded surfaces, whose physical size is small enough to enable the means to be positioned at the extrusion die exit.